Spectrometers are devices that are configured to be able to receive electromagnetic radiation (i.e. light) in a plurality of wavelengths across the electromagnetic spectrum. Such electromagnetic radiation may be imaged by the spectrometer, and may subsequently be utilized in spectroscopic analysis for a number of purposes, including, for example, to perform target material identification based on the spectroscopic signature. The imaging by the spectrometer may be of electromagnetic radiation passed through one or more slits, and accomplished by one or more image sensors assembled at a focal plane for the spectrometer optics. In some spectrometers (generally double-pass spectrometers), the slits and the image sensors may be positioned adjacent to one another at the focal plane for the spectrometer optics. It may be appreciated, however, that depending on the configuration of the spectrometer optics, conventional imaging arrays might be unable to receive the entire field of view that is received by the optics.
FIG. 1 illustrates a schematic of image plane assembly 10 containing image sensor 100, and associated slit 110. Although not shown, it may be appreciated that electromagnetic radiation, focused by fore-optics, may pass through the slit 110 to be emitted out of the plane of the Figure. A spectrometer may then collimate the electromagnetic radiation, break it into its constituent spectra, and then image the electromagnetic radiation into the plane of the Figure, and onto the image sensor 100. Each image sensor 100 may be packaged as part of a sensor chip assembly (SCA) 120, whereby the image sensor is surrounded by associated electronics and interconnects (generically, packaging 130). The image sensor on each SCA 120 may generally contain an array of electromagnetic radiation sensitive elements 140. For spectroscopic purposes, the image sensor 100 may be generally rectangular, having a spatial dimension and a spectral dimension. The image sensors may be elongated in first direction 150, also equivalently known as a cross-track direction, or cross-scan direction, or the spatial dimension. The image sensor may be shorter in length in second direction 160, also equivalently known as the along-track direction, the along-scan direction, or the spectral dimension.
Depending on the field of view achievable by the fore-optics and the spectrometer (collectively the optics field of view) a single image sensor 100 may be insufficient to record all electromagnetic radiation within the optics field of view. Various design constraints on image sensors 100 may be limiting in terms of size and/or pixel density. It may be appreciated that the optics may be associated with a region of image plane assembly 10 that is defined by slits 110 and image sensors 100 thereon. Specifically, the spectrometer optics must be configured to receive electromagnetic radiation from slit 110, disperse it, and redirect it to image sensor 100. As shown, this region may be characterized as theoretical sensitivity region 170. In essence, the spectrometer optics will generally be corrected for image quality and distortion across sensitivity region 170, to limit distortion in the electromagnetic radiation being received from slits 110, and being dispersed and reflected onto image sensors 100.
Accordingly, it may be appreciated that multiple image sensors 100 may be utilized together so as to facilitate recording most or all of the desired or required optics field of view. Because of packaging 130 associated with each image sensor 100, it may be appreciated that multiple image sensors 100 would not be positioned immediately adjacent to one another, but would necessarily be separated by a gap. Accordingly, the size of the gap would be at least the size of packaging 130 associated with each image sensor 100. The gap could also be larger, so as to promote uniformity and symmetry in the arrangement of image sensors 100 at image plane assembly 10. It may be appreciated that such gaps may enlarge theoretical sensitivity region 170 in various designs of image plane assembly 10.
As used herein, the numbering conventions associated with elements of image plane assembly 10 in FIG. 1 may be understood as referring generically to those elements or assemblies, whereby variations on those numbers will apply to similar elements or assemblies. Accordingly, FIG. 2 depicts a conventional “checkerboard design” for image plane assembly 10 (as image plane assembly 10*), configured to utilize multiple image sensors 100* to facilitate imaging over a large field of view provided by the unseen optics. As shown, the checkerboard design of image plane assembly 10* utilizes a plurality of SCAs 120* (including specifically SCA 120a* and SCA 120b*) and associated slits 110* (including specifically slit 110a* and slit 110b*), in a staggered configuration. Each SCA 120* contains an image sensor 100* (including specifically image sensor 100a* and image sensor 100b*) and associated packaging 130* (including specifically packaging 130a* and packaging 130b*). The unseen fore-optics are configured to focus electromagnetic radiation onto the slits 110*, while the unseen spectrometer is configured to receive the electromagnetic radiation from the slits 110*, focus and disperse the electromagnetic radiation into constituent spectra, and direct the spectra onto the associated image sensor 100.
As depicted in the illustrated image plane assembly 10*, to fully utilize the field of view across the combined optics with the checkerboard configuration, the spectrometer must be configured as sensitive and accurate to theoretical sensitivity region 170*, which includes all of slits 100* and the associated SCAs 120* of image plane assembly 10*, including the gaps therebetween. As appreciated from FIG. 2, sensitivity region 170* may exclude some of packaging 130* (namely the bottoms of packaging 130a* and packaging 130* from other SCAs 120* on the bottom row of image plane assembly 10*), as electromagnetic radiation is neither received from nor directed to those portions of the SCAs 120*. While in theory corrections for image quality and distortion are unnecessary between slits 110* and image sensors 100*, for reasons such as cost and efficiency, spectrometer optics design generally does not provide for such intermediate corrections, but rather corrects over broader uniform regions. It may be appreciated that improvements to image plane assemblies 10 may facilitate either a greater field of view for the same level of distortion (i.e. facilitating making the focal planes larger to see more of a given scene at a time), or lower distortion for the same field of view (i.e. increasing performance for the same size of focal plane and optics). Accordingly, what is needed is a construction and arrangement of image plane assembly 10 that facilitates such improvements.